First off, I think what you are doing is great. Documenting how you play and watching your wins and losses is a great way to improve. First tournaments can be a nightmare. I remember my first tournament, and I was as nervous as I could be. I managed to place 4th out of about 15 entrants, which helped bolster my confidence, but I still did not perform anywhere near what I should have.
You will get tournament jitters. Be sure to check out Omni's Tournament Jitters video below:
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Secondly, be sure to play more than 100 for each character. Play absolutely as many as you can squeeze in. Take time to train on the techniques such as short hopping, pivot grabs, pivot attacks. If you are playing Sheik, you have great gimping potential, because of her great recovery. Practice as much as you can off stage. A lot of times I see people not going for off stage kills/gimps because they are not confident in playing off stage. In your video at about the 2:17 mark, you had a prime opportunity to run off the ledge with a back air or possible footstool, at the least you could have charged your needles. Always look for ways to be proactive when waiting on your opponents to do something.
Thirdly, play other stages than Final Destination types. Find out the stage list for the tournament you are going too, and practice on those stages as much as possible, especially the ones you are not comfortable on. This can be hard not having anyone local to play with, but try befriending people in For Glory and setting up matches with them where you can choose your stages.
Fourthly, do not be predictable. I watched your YouTube video and one thing I noticed is that you are predictable with your needles. Just about every time you charged, you shot them out immediately. Save them. Try to hold fully charged needles for at least 10 seconds. Typically opponents will forget you have them. They go a pretty long distance and having them stored up can help gimp an opponent who recovers horizontally.
Good luck at your tournament and post back with how you do!